If you order lattes or macchiatos, you probably like a little sugar (or a similar substitute sweetener) in your coffee. When you order one on the Dunkin' Donuts app it asks you what sweetener you want. Somewhat oddly, the default is none. You are likely quite inclined to change this so you don't get just bitter bean juice you could get far cheaper elsewhere. However, this would be a mistake if you have added one of the sweetened flavor shots. If you turn your drink into a mocha latte and still add the recommended four packets of sugar to your drink, be warned: it will be really, really, really sweet.
The reason for this is that the sweet and flavor shots are intended to replace the sweetener. A large latte's mocha flavor shot contains 45 grams of sugar! The caramel swirl has 51 grams!
You might be able to do this from the name "sweetened flavors", doesn't make it that clear. If you order just a large iced macchiato, it will have 12g of sugar. If you order an iced macchiato and add the recommended amount of sugar, it will have 47g. If you order a caramel iced macchiato, it will have 63g! If you order a caramel iced macchiato and add the recommended amount of sugar it will have 98g of sugar!
While this isn't really a flaw in the app, and it's good to have the flexibility, I think it could be communicated a bit more clearly. Maybe it could add the recommended sugar by default and take it away when you add the sweetened flavor shot, or at least say the recommended amount of sugar for a drink with a sweet and flavor is zero packets.
Regardless, I think it's important for a coffee enjoyer to be aware of what you're really ordering to ensure you get something good. If you don't want flavor and you want sugar, add sugar. If you want flavor and sugar say you want no sugar because the flavor will include it.